feat: add selectAllLabel prop to TableView for customizing the aria-label of the select all checkbox

[zinap-ensemble]

Closes #10529

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices
• I understand every change in this PR and can explain why it's there.
• If AI-assisted, I followed our AI contribution guidance and pointed my assistant at CLAUDE.md.

📝 Test Instructions:

TableView's select all checkbox (selectionMode="multiple" selectionStyle="checkbox") has an aria-label hardcoded to the localized "Select All" string, with no way to override it. This is a problem when a page renders multiple TableViews — every select all checkbox announces identically, so screen reader users can't tell them apart (fails WCAG 3.3.2, see #10529).

This PR adds an optional selectAllLabel prop to TableView to override that label. It's opt-in only — the default "Select All"/"Select" behavior is unchanged for existing consumers, so this is non-breaking.

To test:

1. yarn start, open the TableView stories, select "custom select all labeling".
2. Inspect the header checkbox — aria-label should read "Select all items" instead of "Select All".
3. Compare against the "static" story (no selectAllLabel) — still reads "Select All".
4. With VoiceOver (Cmd+F5) or another screen reader, tab to the checkbox and confirm it announces the custom label.

🧢 Your Project: